You don't say over whet length you are testing or what material you are cutting but a 56mm dia bar in a small lathe will be putting a lot of load on it.

Have you preloaded the bearings as if too loose that would cause the far end to be larger.

Is tool sharp and on ctr height, if not both could be pushing the work away from the tool and giving the big end, particularly if chuck jaws are worn and bell mouthed.

Edited By JasonB on 06/01/2020 19:56:42

Did the lathe turn out of parallel before you removed the spindle and greased bearings and reassembled?

IF not, then the problem is most likely something in the reassembly.

Check the preload adjustment on the bearings again, they may have bedded in some with use. Also, check there is zero measureable up and down or side to side movement of the spindle where the chuck mounts. Do this test with a long bar held in the chuck to yank on, and a dial indicator resting directly on the spindle. With taper roller bearings, should be zero movement.

Nick, as a matter of interest, do your Clamping & Forcing Screws 5 & 6 actually conform to the last illustration? ..only asking because mine are the opposite way round to that..

Thanks for clarifying..

Hi DiogenesII, yes mine are exactly as the illustration is, but I believe mine is an early model, which had two slide switches, and the start/stop one was broken alone with that part of plastic laminate plate that held them. I made a new plate from a piece of Aluminium and moved the forward/reverse switch to the start/stop position and fitted a NVR stop/start in the other position. (see below)

Regards Nick.

If the flange has been removed and replaced, it may be worth just giving it a very light skim to clean it up, to ensure that the chuck sits on a face that is truly square to the axis.

Have you tried clocking it, to check that it is correct in both planes?

Howard

Ah! That's a good starting point! Another possible source of error to be eliminated.

Recently the locknuts came loose on my mini lathe. Although it wasn't one of his, Ketan spent some time explaining to me, the correct procedure to reset the preload. Following his instructions was time well spent.

Little by little you will fix the various possible causes, until it all comes right.

Don't give up!

Howard

Unplug the machine and remove the collar, pulley, gear, and key.

Loosen the rear locking ring and snug the front ring up until play is eliminated at the front bearing – the bearings should not be under load and the spindle should rotate smoothly.

A bar in the spindle/chuck to act as a lever will enable you to check more easily for sideways movement.

Having achieved this, hold the front ring still with the spanner and tighten the rear ring to lock it – it may take a few goes to get it feeling just right – patience is the key!

Replace the key, gear, pulley etc. and test run the machine – it should run smoothly and freely at 2000 rpm, and without getting hot at the bearings (warm after prolonged running is okay).

If it feels stiff, "notchy," or labouring to reach maximum speed, you will have to go back, loosen the rings, and release the bearing load by tapping the back of the spindle towards the tailstock with something soft, such as a piece of wood. Repeat adjustment until satisfied – it sounds laborious, but doesn't take long and is worth doing carefully because the improvement in the feel of the cutting action and the finish on the work are marked on this small machine.

The photo's provided by Nick include the section regarding adjustment of the spindle bearings, such as they are..

The method advised by Ketan applies to the mini lathe (Sieg) so may not apply to other makes.

If you want to know what I did, PM me an with an E mail address, and I'll forward it to you.

BUT bear in mind that this is for another make of machine, and so might overload, or be insufficient for another marque.

Howard